So-called “smart” fluids, such as magnetorheological (MR) fluids and electrorheological (ER) fluids, are fluids that have one or more properties that can change when a given external field is applied thereto. Such external fields may include, for example, a magnetic field in the case of MR fluids and an electric field in the case of ER fluids. The variable properties of such smart fluids may include, for example, viscosity, surface tension, yield stress point, and the like. In the case of MR fluids, an applied magnetic field acts to manipulate the MR fluid, which has micron-sized ferromagnetic particles in a carrier liquid, such as silicone or hydrocarbon oil. Apparent viscosity of the MR fluid can accordingly be varied and thus controlled.
Attempts have been made to use MR fluid dampers as “controllable” shock absorbers that are capable of attenuating vibrations and/or motion to variable degrees by manipulating the MF fluid within the shock absorber, and thus the damping factor of the shock absorber. The shock absorber can thus be made “softer” or “stiffer”, as required, by controlling the strength of the magnetic field to which the MR fluid in the shock absorber is subjected. More specifically, this manipulation of the MR fluid occurs because the ferromagnetic particles in the MR fluid align along the lines of magnetic flux to form chains within the fluid, when the fluid is exposed to a magnetic field. This has the effect of increasing the apparent viscosity of the fluid. Generally speaking, the greater the magnitude of the magnetic field to which the MR fluid is exposed, the more the ferromagnetic particles are aligned, and the higher the apparent viscosity of the fluid—and this for as long as the magnetic field is applied. The stiffness of the damper can thereby be controlled. ER fluid dampers operate in a similar manner, except that the field to which the ER fluid within the damper is applied is an electric field, the strength of which can be controlled as desired to increase or decrease the stiffness of the ER fluid damper.
The MR fluid used in known MR dampers is however typically much denser and heavier than a conventional hydraulic fluid, due to the presence of the ferromagnetic particles in the MR fluid, which therefore increases the overall weight of the damper. While this weight penalty may not be of significant concern for certain applications where weight is not critical, existing MF dampers are less desirable for use in applications in which the weight of the shock absorber is an important factor. Since MR dampers are difficult to scale down in size and/or weight, their use to date has typically been limited to large-scale applications and/or applications which are not weight sensitive.
Furthermore, many existing MR dampers require a continuous electric current be supplied to the electromagnets in order to keep the MR fluid magnetized, and thus so as to maintain an operationally functional damping effect. A similar challenge exists with ER dampers. This imposes a power consumption penalty to the dampers, and further reduces the practicality of such MR or ER dampers for applications in which it may not be possible or desirable to supply a constant source of power to the MR or ER damper.
An improved smart fluid damper is therefore sought.